EP-A-337 239 has already disclosed the use of alkaline earth metal salts of monoesters of dicarboxylic acids and alkoxylated alcohols as catalysts for preparing narrow range alkoxylates. EP-A-657 410 describes the use of alkaline earth metal salts of monoesters of alkylsuccinic or alkenylsuccinic acid and alkoxylated alcohols for the same purpose. In both cases, the unesterified carboxyl group is completely converted into the form of the alkaline earth metal salt. It has now been found that the effectiveness of this type of catalyst can be further improved if the carboxylate group is only partially converted into the salt form.
Such partially neutralized Ca salts of succinic monoesters and their use as alkoxylation catalysts have already been described in U.S. Pat. No. 5,600,020. However, these succinic monoesters are substituted by a C8-C30-alkyl radical. Alkoxylation catalysts of the above-described type based on alkylsuccinic monoesters are, however, obtained as colored products and give colored alkoxylation products. In contrast, the alkoxylation catalysts described below give largely colorless alkoxylation products having a narrow homologue distribution.
The invention provides an alkoxylation catalyst which is prepared by
a) reaction of one mol of a dicarboxylic acid of the formula
HOOCxe2x80x94(CH2)axe2x80x94COOH,
where a is from 1 to 4, with from 1.5 to 8 mol of an alcohol of the formula
Rxe2x80x94(OA)xxe2x80x94OH
where R is C4-C22-alkyl, C4-C22-alkenyl or a group of the formula Fxe2x80x94(CF2)nxe2x80x94(CH2)mxe2x80x94, n is an integer from 6 to 16, m is an integer from 1 to 4, x is from 0 to 6 and A is xe2x80x94C2H4xe2x80x94 or xe2x80x94C3H6xe2x80x94, to form the corresponding dicarboxylic monoester,
b) formation of an alkaline earth metal salt of the dicarboxylic monoester by addition of water and from 0.45 to 0.55 mol of a basic alkaline earth metal compound per mol of dicarboxylic acid originally used,
c) partial neutralization of the alkaline earth metal salt by addition of from 0.25 to 0.7 mol of H2SO4 per mol of basic alkaline earth metal compound originally used and
d) removal of the water present at a temperature of less than 100xc2x0 C.
The dicarboxylic monoester is prepared by methods known per se, as described, for example, in U.S. Pat No. 5,600,020. The reaction is generally carried out at from 70 to 140xc2x0, preferably from 80 to 110xc2x0 C. The molar ratio of alcohol to dicarboxylic acid is from about 1.5:1 to 8:1, preferably from 3:1 to 6:1. Naturally, the corresponding acid anhydride can also be used as starting material in place of the dicarboxylic acid. Preference is given to succinic anhydride. In the case of alcohols of the formula Rxe2x80x94(OA)xxe2x80x94OH, A is preferably xe2x80x94C2H4xe2x80x94.
In the second reaction step, the acidic monoester is converted into an alkaline earth metal salt by addition of a basic alkaline earth metal compound, preferably an oxide, carbonate or hydroxide of barium, strontium, in particular calcium. The amount of basic alkaline earth metal compound is from about 0.45 to 0.55 mol, preferably 0.5 mol, per mol of the acidic monoester or per mol of dicarboxylic acid or dicarboxylic anhydride. Water is added to aid salt formation. The amount of water is not critical but, for practical reasons, an amount of water which is equal to the amount of basic alkaline earth metal compound or is up to three times that is generally employed. Higher amounts of water bring no advantage and merely increase the amount of water which has to be removed again in the final step. To complete salt formation, the mixture is generally stirred for a plurality of hours at from 60 to 100xc2x0 C., preferably from 80 to 95xc2x0 C.
The partial neutralization is carried out by addition of H2SO4 in the amount indicated at from 20 to 80xc2x0 C., preferably from 40 to 70xc2x0 C. Preference is given to using from 0.3 to 0.6 mol of H2SO4 per mol of basic alkaline earth metal compound originally used.
In the final step, the water present is distilled off under reduced pressure, during which the temperature should not exceed 100xc2x0 C. The water is preferably removed under reduced pressure for from 1 to 5 hours at from 50 to 100xc2x0 C., preferably from 70 to 90xc2x0 C. This gives the alkoxylation catalyst in the form of a white, more or less viscous slurry containing the unreacted excess of the alcohol of the formula Rxe2x80x94(OA)xxe2x80x94OH. This slurry can be used directly as catalyst in alkoxylation reactions.
The alkoxylation, i.e. the reaction of compounds containing active H atoms with alkylene oxides using the products according to the invention as catalyst, is carried out in a customary manner, i.e. at a temperature of from 60 to 200xc2x0 C., preferably from 100 to 180xc2x0 C., and a pressure of from about 0.5 to 6 bar, with the alkylene oxide being metered in a little at a time or continuously. The amount of alkylene oxide is generally from 1 to 30 mol, preferably from 2 to 20 mol and in particular from 2 to 15 mol, per mol of compound to be alkoxylated. The alkoxylate obtained can generally be used without prior removal of the catalyst.
According to one variant, the catalyst can be generated in situ. This is done by adding the alkaline earth metal salt produced in step b) to the compound which is to be alkoxylated and then carrying out steps c) and d) in the presence of this compound.
The amount of catalyst of the invention can vary within wide limits and is generally from 0.1 to 5% by weight, preferably from 0.5 to 3% by weight, based on the weight of the compound to be alkoxylated.
Compounds which can be alkoxylated with the aid of the catalyst of the invention are all compounds having an active H atom. Even compounds without an active H atom, e.g. alkyl esters of fatty acids, can be alkoxylated using the catalyst of the invention (insertion of ethylene oxide into the ester group).
Compounds containing active H atoms are, for example, hydroxyl-containing compounds, amine compounds and acid compounds such as fatty acids, with preference being given to the former. Examples of hydroxyl-containing compounds are alcohols, aminoalcohols, perfluoroalkyl alcohols, glycols, glycol monoethers, glycerol, phenols, cresols, and the like, with preference being given to alcohols. They can originate from natural sources or from synthetic processes and be primary, linear or branched, saturated or unsaturated, monohydric or polyhydric, for example, oxo alcohols, Guerbet alcohols, Ziegler alcohols, fatty alcohols, fluoroalcohols and the like. Preferred alcohols are primary, straight-chain or branched C3-C24-alkanols, preferably C6-C18-alkanols (fatty alcohols) or mixtures thereof, for example mixtures of C12- and C14-alkanol (C12/14), and also perfluorinated alcohols. Examples of preferred alcohols are: butanol, amyl alcohol, hexanol, nonanol, isononyl alcohol, decanol, undecanol, isoundecanol, lauryl alcohol, isotridecyl alcohol, stearyl alcohol, coconut fatty alcohol and mixtures thereof, also 2-ethylhexanol, 2-hexyldecanol, 2-octyldecanol and similar Guerbet alcohols.
As alkylene oxides, preference is given to using ethylene oxide, propylene oxide and/or butylene oxide, with ethylene oxide being preferred.
The alkoxylation catalyst prepared according to the invention has a high catalytic activity and, in a relatively short reaction time, leads to virtually complete conversion and to a high yield. The alkoxylate has a narrow homologue distribution and is colorless and frequently clear and thus has a good appearance.
In particular, the ethyoxylation of alkyl esters of fatty acids gives, due to the narrow homologue distribution and the high degree of conversion, more uniform products and less by-products compared to conventional catalysis using basic Na or K compounds.